NEAR-EARTH ASTEROID 2004 MN4

Precise determination of the orbit (and future location)
of an asteroid or comet typically requires
measurements of its position and motion in space over
a period of many months to years.
Naturally for a newly discovered asteroid or comet,
the time baseline for these position and motion
measurements is limited by the recentness of the discovery.
Consequently, orbit calculations based on these limited
data can yield only preliminary results. In some cases,
these preliminary results may indicate one or more
future close approaches with the Earth for which
the possibility of a collision is not completely
ruled out.
Because the results of these orbit calculations
are only preliminary, they are subject
to revision as new data become available.

The
International
Astronomical Union Working Group on Near Earth Objects
(WGNEO) provides, as a service to the international
astronomical community, expert review of reports of
newly discovered objects for which preliminary orbit
calculations indicate some possibility of a
collision on a future date.
Individuals and organizations are free to make
their discoveries, observations,
and calculation results public at any time.
If they so choose, the discoverer or the scientist(s)
producing the orbit calculations may voluntarily
submit their report to the WGNEO for
Technical Review.
The purpose of the WGNEO Technical Review
is to provide independent expert verification
of the preliminary orbit solution
based on all currently available data.

This
IAU WGNEO
announcement pertains to a
near-Earth object designated as 2004 MN4.
This object was discovered on 19 June 2004 by Roy Tucker, David Tholen
and Fabrizio Bernardi of the University of Hawaii
Asteroid Survey (UHAS), from Kitt Peak, Arizona, and
observed over two nights.
Most likely this object is a small asteroid about
400m in diameter. On 18 December, the object was rediscovered
from Australia by Gordon Garradd of the Siding Spring Survey.
Further observations from around the globe over the next several
days allowed the
IAU Minor Planet Center
to confirm the connection
to the June discovery.
Orbit calculations based on the observed path over the period
19 June through 27 December were performed
and cross-verified by two separate systems,
CLOMON2
in Pisa/Valladolid and
Sentry in Pasadena,
where this cross verification satisfied the requirements for a
Technical Review.
Beginning with observational data available on 23 December,
these solutions indicated a non-negligible
impact probability with the Earth corresponding to a
value of 2 on the 10 point
Torino Scale.
Continual updates to these
solutions were performed as new data were obtained, with these
ongoing preliminary results giving a chance of as much as
about 1 in 40 for a collision with Earth on 13 April 2029.
This collision probability corresponded to a
4 on the 10 point
Torino Scale, which describes Level 4 as:

"A close encounter, meriting attention by astronomers.
Current calculations give a 1% or greater chance of
collision capable of regional devastation. Most likely,
new telescopic observations will lead to re-assignment
to Level 0 [No Hazard]. Attention by the public and by
public officials is merited if the encounter is less than
a decade away."

These calculations also indicated a value of about +1.0 on the
Palermo Technical Impact Hazard Scale,
meaning that the potential 2029 impact was about ten times
more likely than a random impact of a similar-sized object
before 2029.

As appropriate for the
Torino Scale
4 rating,
astronomers continued their routine positional measurements of 2004 MN4
so as to extend its orbital arc over a longer baseline to allow further refinement
to its orbit and to the Earth close approach situation in 2029. At the same time,
astronomers also methodically searched through archives to locate "prediscovery"
observations made prior to June 2004. These archive search efforts proved successful
on 27 December when Jeff Larsen and Anne Descour of the Spacewatch Observatory near
Tucson, Arizona, were able to detect and measure very faint images of
2004 MN4 on archival images dating to 15 March 2004. These observations
extended the observed orbital arc for this object by an additional three months.
The resulting improvement to the orbit solution allowed any chance of
an Earth impact on 13 April 2029 to be ruled out, reducing the hazard index
for this encounter to 0 [No Hazard] on the
Torino Scale.
The current orbital solution also indicates that no future
Earth close approaches by 2004 MN4 during the 21st century rank
higher than 1 ["Normal"] out of 10
on the
Torino Scale. These 21st century encounters also merit a
score of -2.0 or less on the
Palermo Technical Impact Hazard Scale,
meaning that a random impact of a similar-sized object
is about 100 times more likely than a 2004 MN4 impact.